Absorber

ABSTRACT

An absorber is provided which uses a liquid solvent formed into a myriad of bubbles and micro-droplets. The solvent froth is a solvent for a selected component in an incoming gas stream. A plurality of spaced apart mesh assemblies is placed in one or more absorber tubes or in a reaction vessel. Using screens having cross-sections that are substantially rectangular wave in design together with proper operating parameters, the phenomenon of solvent pulsing is induced and maintained, maximizing efficiency of the absorber.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation-in-Part of U.S. application Ser. No.13/385,305 filed Feb. 13, 2012.

BACKGROUND

Typical prior art absorbers utilize what is described herein as astatic, fixed surface area on which the absorption occurs. For example,a common absorber design is a “shaped packing” design. In this design,packing elements with complex surface shapes are placed in a fixed sizechamber. A liquid solvent is typically caused to flow downwardly and wetthe fixed size exterior surfaces of the elements. This provides a largesurface area for mass transfer between the solvent and the gas. A gas isthen driven upwardly through the packing, and a selected component ofthe gas is absorbed into the surface of the solvent. The surface area ofthe packing remains fixed and static. The three commercial types ofpacking are random, structured trays, and spray towers. The fixed andstatic surface area is a major limitation of the prior art.

Another common limitation of known absorbers is the relatively shortamount of time in which the two fluids are in surface contact with eachother. The prior art designs typically use a counter-flow arrangementwherein the solvent in the above specific shaped packing example flowsdownwardly and the gas flows upwardly. The counter-flow technique isutilized to maximize the concentration gradient between the two fluidsbut has the inherent limitation of minimizing the time in which thesurfaces of the two fluids are in contact.

A further limitation of these conventional packings is the significantheight of packing required to facilitate the absorption process. Afurther limitation of most prior art absorbers is that they requirerelatively expensive materials in their construction. The large surfacearea of these packings which is required to facilitate absorption alsomakes them susceptible to fouling where the surfaces can become fouledwith dirt, impurities from the gas or liquid or precipitation productsfrom the absorption itself.

The present invention overcomes all of the above limitations of theprior art.

BRIEF SUMMARY OF INVENTION

The present invention not only overcomes the above limitations of theprior art; the applicants have identified and utilized in the mostpreferred embodiment the hydrodynamic phenomenon described below as“solvent pulsing.” This phenomenon significantly enhances absorptionefficiency in the absorber described herein. We have been able tosuccessfully induce “solvent pulsing” by using the system describedbelow. We believe that the absorber described below is the first frothbased absorber to induce and maintain “solvent pulsing” to maximizeefficiency.

The present invention, in contrast to using the prior art static, fixedsurface area, creates dynamic, rapidly changing, large surface area fora given volume. Solvent bubbles and droplets are intentionally caused toburst and are formed and shattered, at a rapid rate. The objective is tocreate the densest possible array of the smallest bubbles, droplets andmicro-droplets and to repeatedly, rapidly and violently cause each ofthem to break up or fragment. The mass transfer surface is greatlyincreased and constantly refreshed, thereby maximizing the mass transfer(or absorption) within a given volume of an absorber reaction chamber.The contact environments range from an aqueous-froth column with amicro-froth matrix that is reformed at high frequency, to a transientfroth that alternates at high frequency from a micro-froth matrix to aprojectile spray fueled by bursting bubbles, to a shear-spray withisolated membrane rupture and impact fragmentation. Each of thesedynamic mass transfer processes provide a high reactant surface area anda dramatic increase in absorption efficiency compared to conventionalgas/liquid absorbers.

The present invention uses specially shaped and spaced apart screens tofragment the solvent froth into a myriad of droplets which creates avery large surface area for mass transfer, which surface is made up ofthe solvent itself. But instead of leaving the small droplets intact ina confined space which would produce a relatively static, fixed surfacearea similar to prior art devices, the present invention continuouslyand violently fragments and reforms the droplets at a rapid rate.Bubbles also form which in turn are caused to burst, forming thousandsof microscopic droplets from each bursting bubble, whereby the activesurface area of the liquid solvent is further increased. This highfrequency and continuous regeneration of the surface of the liquidsolvent is a significant aspect of the invention. An enormous reactionsurface is created in a small volume. The reaction surface iscontinuously and violently ruptured and reformed to maximize theefficiency of the mass transfer.

The present invention also differs significantly from the prior art inthat it maximizes the time period of contact between gas and solvent byusing a concurrent (or co-current) flow as opposed to a counter flowtechnique. By maximizing the time period of contact, we inherentlymaximize the efficiency of the absorption process. The time period ofcontact may be further extended by using multiple stages in the process.

The present invention, by continuously and rapidly regenerating thesurface area of the solvent maintains a maximized concentration gradientacross the entire surface of the solvent for the entire time period inwhich the gas and solvent are in contact with each other, all for thepurposes of mass transfer. Any given droplet or bubble will interactwith the gas across its entire surface momentarily, and then as thebubbles burst as they pass through the next screen, many droplets arefragmented into micro-droplets, some droplets coalesce and are thenreformed as the liquid is forced through the screen. Each time thisprocess is repeated the freshly formed surface provides a new leansolvent surface area to interact with the gas with a maximizedconcentration gradient, since the surfaces of the bubbles, droplets, andmicro-droplets do not remain intact long enough to become saturated withthe component being removed or absorbed from the gas.

In addition to the above advantages, the applicants have identified andutilized, for the first time in a froth-based absorber, the hydrodynamicphenomenon referred to herein as “solvent pulsing,” which substantiallyincreases absorption efficiency. Although overall liquid-gas molar flowrate ratios are comparable to conventional contactors, solventvolumetric flow rate in the present absorber is not constant. Rather,solvent volumetric flow rate initially is low and a fraction of thesolvent accumulates in the pulsing screens described herein. Uponreaching a critical saturation, a large fraction of the accumulatedsolvent travels downstream at high volumetric flow rate in a pulse.After the pulse, the solvent volumetric flow rate is low again untilanother pulse occurs. This repeats ad infinitum. This pulsing isbeneficial because at flow rates and liquid-gas ratios similar to thatof conventional columns the Reynolds number for the liquid places itsquarely in the laminar regime. However, because the absorberexperiences the pulsing phenomenon, it greatly increases the volumetricflow rate during a pulse bringing it more in line with turbulent flow.There exists numerous literature that show turbulent flow causes bettermixing. Furthermore, high speed photography shows pulsing enhancing theformation of micro-froth. Literature also exists that show froth andbubble structures enhance contact area. The use of co-current flow andthe geometry of the screens allow for these important solvent pulses tooccur.

In the embodiments where precipitating solvents are utilized, thepresent invention also prevents clogging of the reaction vessel byprecipitants. This “anti-clogging” feature is achieved by constantlyreforming the solvent froth to minimize the size of solvent bubbles inthe froth, thereby minimizing the size of precipitants and preventingclogging of the reaction vessel.

The present invention also differs significantly from the prior art inthat less materials can be used to fabricate the absorber of the presentinvention.

The present invention also represents a significant improvement overexisting absorber systems. An inherent limitation of such absorbers isthe efficiency and physical size of the absorber. As the liquid streamtrickles down through the packing any non-uniformity in the packing ormaldistribution of the liquid onto the packing or the absorber itselfnot being perfectly level will cause channeling of the liquid. Thischanneling or maldistribution will reduce the effective surface area ofthe packing available for mass transfer thereby reducing the efficiencyof the absorber. To prevent this, packing bed heights are limited to 5to 10 m and require redistributors for the gas and liquid between packedsections.

The present invention includes a technique which eliminates “channeling”and also simultaneously increases the efficiency of absorbers and allowsfor the absorbers to be any shape. The present invention in someembodiments utilizes an array of tubes strategically placed in thereaction chamber; the tubes force the gas stream to divide itself intosmaller, equally sized sub streams to flow through the array of tubes.This technique causes all portions of the gas and liquid streams to beequally distributed thus eliminating the problems of channeling ormaldistribution associated with conventional absorbers and allowing forabsorbers of significantly larger diameter than absorbers usingconventional packing. These tubes can be round, square, polyhedral oralmost any geometric shape.

In yet another embodiment the tubes may be replaced altogether withcontinuous packs of corrugated and/or flat screens which fill the fulldiameter of the absorber vessel. These “packs” would be held in place bysupporting rings and grids and solvent would be dispersed evenly ontothe top of the packs using any one of a number of conventional liquiddistributors.

The use of the above techniques together in combination in the mostpreferred embodiment provides, for the first time known to applicants auniversal absorber that can be utilized with virtually any gas andliquid. The combined use of:

-   -   a continuously regenerated reaction surface area created by        rapidly and continuously forming solvent droplets and bubbles,        bursting bubbles and fragmenting or shattering droplets to form        further micro-droplets;    -   maintaining a maximized concentration gradient over the entire        reaction surface during the entire reaction time period;        maximizing the time period of the reaction by use of concurrent        flow; and    -   utilizing “solvent pulsing” to enhance efficiency; results in        forming a new universal absorber that overcomes the above noted        limitations of prior art absorbers.

A primary object of the invention is to provide an absorber utilizingthe features described in the preceding paragraph to improve absorptionefficiency.

In an alternate embodiment an array of properly placed tubes is used inthe reaction chamber to prevent channeling of plumes, increase overallefficiency and to allow the use of large, efficient froth reactionchambers (more than 15 meters in diameter for a cylindrical chamber).

A further object of the invention is to provide an absorber capable ofuse with large reaction chambers, but which eliminates channeling. Otherobjects will become apparent from the following description anddrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustration of an absorber referred to herein asa “flooded tube gas absorber” (FTGA), shown in a sectional view;

FIG. 2 shows a single shaped screen with a square wave cross-section;

FIG. 3 is a section on the line 3-3 of FIG. 2;

FIG. 4A shows an absorber tube with a row of rectangularly shaped holes;

FIG. 4B illustrates two absorber tubes with their tops aligned;

FIG. 4C shows an absorber tube with a notched top over which solventflows;

FIG. 4D shows an absorber tube with a series of holes formed on ahorizontal line in its side wall through which solvent flows;

FIG. 4E shows an absorber with two horizontal, vertically spaced apartrows of holes;

FIG. 5 is a schematic cross-section of an alternate absorber wherein“full diameter” screen packs are utilized;

FIG. 6 shows a screen pack utilized in the absorber of FIG. 5;

FIG. 7 shows a plurality of corrugated screens;

FIG. 8 shows a single corrugated screen;

FIG. 9 illustrates an alternate absorber design utilizing pressurizedsolvent;

FIG. 10A is a schematic cross-section of an alternate embodiment whereinno absorber tubes or bulkhead plates are utilized; rather a conventionalsolvent distributor provides solvent to a plurality of spaced apart,square shaped screens;

FIG. 10B illustrates the use of two reaction vessels of FIG. 10A fed bya common inlet duct;

FIGS. 11A-11F illustrate the technique of “solvent pulsing” with thedynamic, rapidly changing absorption surface;

FIGS. 12-15 illustrate various screen cross-section designs which may beutilized with absorbers described herein.

FIGS. 16A-16F illustrates how solvent accumulates on the screens and howsolvent pulses are created;

FIG. 17 is a graph illustrating screen parameters for inducing “solventpulsing;”

FIG. 18 is a graph illustrating the increased absorption efficiency whensolvent pulsing is utilized, compared to a non-pulsing or trickle flowmode;

FIG. 19 is a graph illustrating increased efficiency of co-current flowutilized herein compared with prior art counter flow absorbers;

FIG. 20 is a schematic illustrating how “solvent plug pulses preventchanneling.

FIG. 21 is an illustration of the prior art problem known as“channeling;”

FIGS. 22 and 23 are photographs of an absorber of the present inventionshowing that when solvent froth accumulates on a screen, the frothoccludes light being directed transversely through the absorber; and

FIG. 24 illustrates how the photographs of FIGS. 22, 23 were taken.

DETAILED DESCRIPTION OF THE DRAWINGS Description

We define important phrases used herein and in the claims as follows:

As used herein and in the claims, the phrase “solvent pulsing” means theperiodic, abrupt and violent separation of clumps of accumulated solventbased froth and micro-droplets from a tier of shaped screens, occurringat frequencies of between 1 and 20 cycles per second. The solvent pulsesmove through the reaction chamber in a “stop and go” fashion, as opposedto a trickle flow or laminar flow. When “solvent pulsing” has beeninduced and maintained, turbulence within the reaction chamber has beenmaximized.

The phrase “substantially rectangular wave cross-section” as used inthis specification and in the claims shall mean a cross-section having aplurality of waves as illustrated in FIG. 12-15; wherein each wave isrectangular, has a flat top surface and a flat bottom surface, each ofwhich lies in a plane within 5° of being perpendicular to the gas streamflow direction; and wherein each top surface has two sidewalls extendingdownwardly, and each side wall is flat and lies in a plane within 5° ofthe gas stream flow direction.

FIG. 1 shows the first embodiment of the invention, referred to hereinas a “flooded tube gas absorber” (FTGA). The bubbly, solvent frothformed in absorption tubes 40 is not shown for clarity. It includes areaction or absorber vessel 20 which as shown is a cylindrical,vertically extending vessel, which may, in some uses, exceed 15 metersin diameter. Reaction or absorber vessel 20 may be virtually any shape,and have cross-sections which are circular, oval, rectangular,polyhedral, or other shape.

An incoming, flow gas stream 30 such as flue gas from a fossil fuelpower plant, flows into inlet duct 31 connected to inlet port 33 at thetop or upper end of vessel 20. Gas stream 30 contains a selectedcomponent, such as CO2, for example, in the case of a flue gas stream,to be absorbed. Incoming flowing gas stream 30 flows downwardlyvertically through reaction or absorption vessel 20, and after beingsubjected to the absorption process described herein, is dischargedthrough outlet duct 32.

Reaction vessel 20 has a first chamber 25 and a second chamber 26separated by bulkhead plate 21 extending horizontally across verticalreaction vessel 20. First chamber 25 is fluidly connected to gas inletduct 31 to allow flow of pressurized gas stream 30 into first chamber25. Bulkhead plate 21 extends across outlet end 25 b of first chamber 25to separate first chamber 25 from adjacent second chamber 26.

A plurality or array of discrete, vertically oriented absorption tubes40 is carried in respective flow ports 40 a formed through bulkheadplate 21. Each of the absorption tubes 40 extends through bulkhead plate21 into first chamber 25 to define a respective conduit for the flow ofgas stream 30 from first chamber 25 into second chamber 26. These tubesbeing of any one of a number of possible geometric shapes. The flowports 40 a and absorption tubes 40 are sized and positioned to equalizethe flow speed of gas stream 30 downwardly through each absorption tube40 from first chamber 25 into second chamber 26.

Fan 97 constitutes means for pressurizing gas stream 30 in first chamber25 to cause a back pressure in chamber 25, which in turn causes gasstream 30 to flow at substantially the same, equal flow rates througheach of the absorption tubes 40 into second chamber 26, therebyeliminating the prior art problem of “channeling” (see FIG. 21 anddescription below).

As shown in FIG. 1, an optional second bulkhead plate 23 (identical toplate 21) is placed below first bulkhead plate 21 to form an additionalset of chambers 27 and 28 which are identical to the chambers 25, 26.

An array of discrete, vertically oriented absorber tubes 40 are denselymounted to and carried in flow ports 40 a in the bulkhead plates 21 and23. The gas absorber tubes 40 are mounted perpendicular to the plates21, 23 and parallel with the vertical axis of the vessel 20. The numberof gas absorber tubes required on each stage is dependent on the gas andliquid flow. Each stage may include one tube or many thousands of tubes.Each of the absorption tubes 40 extends through bulkhead plate 21 todefine a respective conduit for the flow of gas stream 30 from firstchamber 25 into second chamber 26. The tubes 40 and ports 40 a carryingtubes 40 are sized and positioned to equalize the flow speed of gasstream 30 downwardly through each tube from first chamber 25 to secondchamber 26.

Lean liquid solvent is fed into the absorber above plate 21 by inletlines 51 to flood the space above bulkhead plate 21 and between thetubes 40 forming a solvent reservoir 56. Liquid solvent 50 may be anysolvent capable of absorbing the selected component, CO₂, in the examplegiven. Each tube 40 carries a screen assembly 60 described below.Solvent then is injected through holes and/or the slots 41 into each ofthe tubes 40 onto a screen assembly (or froth generator) 60 to mix withthe gas stream 30 and establish froth droplets and bubbles (both notshown for clarity) inside tubes 40. Alternatively solvent may simplyflow over the top of the absorber tubes negating the need for holes orslots. In these cases the top of the tubes may have notches (FIG. 4C) toallow the solvent to drain at set points into the tube or the tube lipmay be even creating an even solvent flow over the entire top of thetube. Each of these techniques injects liquid solvent into each of theabsorption tubes 40 and through a plurality of mesh screens 60 providedin each tube 40 to form an aqueous bubbly froth from said liquid solventinside each of the absorption tubes 40 as gas stream 30 flows throughthe tube 40. Each mesh screen extends transversely between side walls ofeach tube 40.

Each tube is fitted with an array of screens as described below. Thesescreens act to burst, shatter, fragment or break up the bubbles in theaqueous froth into a myriad of droplets and micro-droplets of differentradii which creates a very large, rapidly changing solvent surface, asdescribed in detail in U.S. Pat. No. 7,854,791, incorporated herein byreference. The solvent bubbly froth and micro-droplets are not shown inthe drawings herein for clarity. The screen assemblies shown in FIGS. 2,3, 6, 10A, 10B and 12-15 may be utilized in tubes 40. Each of thoseassemblies has a plurality of vertically spaced apart mesh screens. Eachscreen may have any of the preferred cross-sections shown in FIGS.12-15, as well as any shaped screen or corrugated screen as describedbelow.

The injection of solvent into each of the absorption tubes may be doneby various techniques described herein, all of which will form anaqueous froth in each absorption tube, in a manner that the screenassemblies cause bubbles in the froth to burst, reform, and burstrepeatedly to form numerous micro-droplets of different radii, therebycreating a rapidly changing surface area for absorption.

In some cases in order to deliver the leanest solvent to each stage thelean solvent may be fed directly to each stage (line 52). In this casethere would be a separate lean solvent feed line to each stage and aseparate dehydration stage below each absorber stage.

Where separation of the gas and liquid is required, multiple liquid/gasseparators are mounted directly below the tubes. One possible form ofthese separators is shown, but others exist. The passageways through theliquid/gas separators establish fluid (gas) communication between theinitial dewatering chamber 26 and a next absorber stage 27 of theabsorber vessel. In this step the liquid falls and settles into thespace between the separators and can then be drawn off as a continuousliquid stream through a rich solvent drain line 53 to be regeneratedinto lean solvent. The gas 30 in turn passes through the separator tubesand into the next absorber stage. The need to remove the liquidabsorbent after each absorber stage is dependent on the requirements ofeach application.

In other cases all the lean solvent will enter the absorber via a singleline at the top of the absorber and will pass through the multiplestages of the absorber to be removed at the bottom or absorber sump.

The gas and liquid leaving the tubes flows into the next stage in theabsorber.

In applications where liquid absorbent removal is not required, thepartially spent absorbent from the first stage will fall into theliquid-absorbent reservoir of the next stage, and in-turn enter the gasabsorber tubes.

The final dehydration stage 28 includes a rich-solvent reservoir 29 inthe bottom of the vessel 20. A horizontal gas outlet duct 32 projectsthrough the vessel wall in the final dewatering chamber to allow the gas30 to leave the absorber vessel 20.

Fresh or lean solvent 50 is delivered to the absorber through inlet line51 and in the case of multiple inlets 52 and others.

Rich solvent 55 (the solvent already used to absorb components from thegas) exits through drain 57 at the bottom of vessel 20 and is directedto a solvent regeneration system which is not the subject of this patentapplication.

The solvent regeneration system uses heat and/or a vacuum to strip thecomponent which has been removed from the gas stream from the solvent sothat the regenerated solvent can in turn be reused in the absorber.

FIGS. 2 and 3 illustrate a circular screen 68. The mesh filaments 68 aand 68 b are woven perpendicularly to each other and have linear axesA-A and B-B. Substantially rectangular or square waves (see FIG. 3B) 68c, 68 d and 68 e are formed in screen 68, having axes C-C. The C-C axes68 c-68 e preferably form a 45° angle with the linear axes A-A and B-Bof screen filaments 68 a and 68 b, respectively.

FIG. 4A-4E illustrates various absorber tube designs. Each of theseabsorber tubes can be utilized with various screen assembly designsinside the absorber tube. Each of these tube designs, working togetherwith solvent reservoir 56 (FIG. 1) comprise means for injecting liquidsolvent 50 downwardly into each absorption tube 40.

FIG. 4A illustrates a tube 940 having a row of rectangular slots 941formed in its side wall; solvent flow through slots into tube 940.Screen assembly 960 is mounted inside tube 940 below row 941.

FIG. 4B illustrates an absorber tube 540 design wherein the tops oftubes 540 are aligned horizontally, and solvent simply flows into thetop of each tube as shown by the insert in FIG. 4B.

FIG. 4C illustrates two absorber tubes 540 wherein notches are formed inthe top of the tubes, allowing solvent to flow through the notches intothe tube. Tubes 540 extend above bulkhead 521 in reaction vessel 520.

FIG. 4D illustrates a tube 740 with holes 741 formed in the side wall ofthe tube; solvent flows through holes 741 into the tube 740. A screenassembly 760 with three corrugated screens 761 a, 761 b and 761 c ismounted inside tube 760 below holes 741.

FIG. 4E illustrates a tube 840 with two, horizontal, vertically spacedapart rows of holes 841 a and 841 b. Screen assemblies 860 a and 860 bare mounted inside tube 840 below rows 841 a and 841 b, respectively.

FIG. 5 illustrates another embodiment in which the tubes may be replacedaltogether with continuous packs of corrugated and/or flat and/orsubstantially rectangular wave shaped screens which fill the fulldiameter of the absorber vessel. These “packs” are held in place bysupporting rings and grids and solvent are dispersed evenly on to thetop of the packs using any one of a number of conventional liquiddistributors. This embodiment is referred to as herein as the “FullDiameter Screen” embodiment.

FIG. 5 shows a vertical reaction vessel 220 through which a gas stream230 flows downwardly. Rather than using the array of absorber tubes 40as shown in FIG. 1, the embodiment shown in FIG. 5 uses “screen packs”260 in which the individual screens extend from side wall 220 a to sidewall 220 b. A liquid distributor 280 distributes solvent evenly over thetop of “screen pack” 260. In other respects the absorber vessel 220 isthe same as vessel 20 of FIG. 1. Fan 297 pressurizes gas 230 as it flowsthrough vessel 220.

FIG. 6 shows schematically how “screen pack” 260 is positioned betweenwalls 220 a and 220 b of vessel 220 shown in FIG. 5. Each of the screens261 a-261 e is corrugated preferably and the axes of corrugation areoffset as much as 90° from adjacent screens. Screens 260 are held inplace by supports 266.

FIG. 7 shows a screen assembly 160 where corrugated screens 167 a-167 eare used. The assembly may consist of flat or corrugated screens or acombination of both types. It is significant to note that the axes ofthe corrugations in screens 167 a-167 e are rotated relative to eachother. For example, the axis X-X of the corrugations of screen 161 b isrotated counter-clockwise about 45° relative to the axis of corrugationsY-Y of screen 161 a. Adjacent screens are preferably offset or rotatedso that their axes of rotation are offset between 45° and 90°, and mostpreferably from 60° to 80°.

FIG. 8 is a perspective view of a single, circular, corrugated screen 67that may be used in the screen assembly 160 of FIG. 7 or assembly 260 ofFIG. 6. Screen 67 has a sinusoidal cross section 67 a.

FIG. 9 illustrates an alternate embodiment wherein a verticalarrangement of absorber tubes 440 in FIG. 8 can be modified for use asshown by tubes 1440 with the vertical vessel 1420 shown in FIG. 9.O-ring seals (or other seals known in the art) 1490 are either placed orwelded between each absorber tube 1440 and bulkhead plates 1421 a and1421 b. The chamber 1485 between bulkhead plates 1421 a and 1422 b ispressurized. Pressurized lean solvent is fed through line 1451 intochamber 1485 and into absorber tubes 1440 through openings 1441 formedin the walls of tubes 1440. Fan 1497 pressurizes vessel 1420.

The Solvent Pulsing Phenomenon

FIG. 10A illustrates an embodiment of the invention wherein the solventpulsing phenomenon is described. The absorber shown generally as 1310includes a vertically extending, single chamber reaction vessel 1320.Only the upper portion of vessel 1320 is shown in FIG. 10A for clarity.The lower portion of vessel 1320 includes a solvent reservoir and outletduct as shown in the lower portion of FIG. 1. Reaction vessel 1320 hasan upper inlet 1331 into which incoming flowing gas stream 1330 flows.Fan 1399 pressurizes gas stream 1330 as it flows through vessel 1320.Gas stream 1330 flows downwardly through reaction vessel 1320 and isdischarged through a lower outlet (not shown) similar to outlet 32 ofFIG. 1 after being processed in reaction vessel 1320.

Incoming flowing gas stream is pressurized by any conventional fan 1399or other known device.

Reaction vessel 1320 carries a plurality of vertically spaced apart,shaped screens 1360, each having preferably substantially rectangularwave cross-sections, wherein each screen extends transversely acrosssaid reaction vessel. The screens extend from sidewall 1321 to side wall1322 and extend completely across the cross section of reaction vessel1320. The screens are vertically spaced apart by spacers 1366. Thescreens are shown aligned for clarity, but may be offset in relation toeach other. Screens 1360 may have substantially square cross-sections orother screen designs shown herein.

A solvent injector 1355 mounted inside vessel 1320 near the top of thevessel distributes a liquid solvent 1350 that is fed in through inletline 1351. As shown in FIG. 13A, the distributor has a spider type head1356 which distributes liquid solvent 1350 a downwardly into reactionvessel 1320.

The liquid solvent 1350 a flows downwardly through reaction vessel 1320co-currently with gas stream 1330.

The interaction of the incoming gas stream 1330 with the liquid solvent1350 a and screens 1360 creates an aqueous bubbly froth being intermixedwith numerous micro-droplets formed from causing bubbles in the froth toburst, as described generally above and described in detail in U.S. Pat.No. 7,854,791 and is not described or shown here for the sake of brevityand clarity.

FIG. 10B illustrates the upper portion of two reaction vessels identicalto reaction vessel 1320 of FIG. 10A fed by a common inlet duct 1331 a.Solvent distributors 1355 a and 1355 b are identical to distributor 1355of FIG. 10A, and are fed solvent 1350 a by feed line 1351 a. FIG. 10Bshows that an array of absorbers such as absorber 1310 of FIG. 10A maybe fed an incoming gas stream and solvent from common ducts and feedlines. Fan 1399 pressurizes gas stream 1330.

We have found that by utilizing shaped screens having preferablysubstantially rectangular wave cross sections, together with certainflow rates of the incoming gas stream, we have identified and we havebeen able to induce and maintain the phenomenon described herein as“solvent pulsing.” This phenomenon is illustrated schematically anddescribed below and is used in the absorbers shown in FIGS. 10A and 10B.Solvent pulsing can also be used as an optional feature in all of theabsorbers described herein.

FIGS. 11A-11F— are concept sketches, not to scale that illustrate the“solvent pulsing” phenomenon created in the upper portion 1321illustrated in FIG. 10A. A section of screens 1360 near the top ofreaction vessel 1320 are shown in 11A-11F. The screens 1360 are shown asbeing aligned for clarity, but are preferably offset as describedherein. The screens shown in FIG. 10B use screens having substantiallysquare cross sections.

FIG. 11A illustrates solvent flow 1355 initially in the system. It is atrickle of solvent flowing down the column in a laminar fashion.

FIG. 11B illustrates the beginning of solvent froth accumulation 1356beneath the tops the screens 1360 a and 1360 b. Accumulation occurs nearthe very top of the column and solvent flow rates 1355 a decrease as aportion of the flowing solvent accumulates.

FIG. 11C illustrates a near saturation of screens 1360 a, 1360 b withsolvent froth 1356 a, with the lowest solvent flow rate 1355 b.

FIG. 11D illustrates all the accumulated solvent 1356 b being releasedabruptly from screens 1360 a and 1360 b and traveling downstream in ahigh velocity turbulent solvent pulse 1356 b. We have observed thatoften the “solvent pulsing” will occur across the entire width of screen1360, as shown in FIG. 11D. We describe such a pulse as a “solvent plugpulse” since it extends across the screen 1360 and moves downwardlythrough the reaction chamber as a “plug.” Multiple “plugs” will bemoving downwardly through the reaction chamber simultaneously. These“plugs” prevent “channeling” in the reaction chamber as described below.

FIG. 11E illustrates flow returning to a similar fashion as in FIG. 14A;once again a trickle of laminar solvent.

FIG. 11F illustrates accumulation beginning again, as in FIG. 14B; andthe cycle repeats itself.

Screens

The screens of the embodiments shown in FIGS. 10A and 10B are fabricatedfrom woven wire mesh or screens. The cross-sectional area of the screensis arranged perpendicular to the vertical axis of absorber tube so thatthe gas and liquid flow through each screen in sequence. The preferablysubstantially rectangular wave shaped screens (shown in FIGS. 10A and10B as substantially square wave shaped screens having vertical sidewalls, flat tops, and flat bottoms of equal length in order to reducepressure drop and increase liquid-gas interfacial area. The linear axesof the screen mesh filaments are aligned at a 45 degree angle to thelinear axis of the ridges as shown in FIG. 2 above. The preferredsubstantially rectangular-wave shaped screens increase liquid hold-upand introduce turbulence into the flow field. The square-wave screensenable pulsing of liquid structures, aeration of the liquid pulses, andfroth matrix formation. The linear axes of the screen filaments of eachscreen are rotated between 45° to 90°, and preferably between 60° and80°, in reference to the linear axis of the ridges of each upstreamscreen in order to keep the liquid phase distributed evenly over thecross-sectional area of the screens throughout the reaction chamber. Theclosely-spaced screens reform the reactant surfaces at high frequency inorder to maximize fresh reactant surfaces exposed to the target gas.

In the preferred embodiment of FIG. 10A, an assembly of ten (10)substantially rectangular-wave shaped screens with 12×12 openings/squareinch, 0.055″ apertures, 0.028″ wire diameter, and 44% open area areseparated by thin annulus shaped spacers, 0.25″ thick, that support thescreens around the periphery of the absorber tube. The‘pulse-generation’ screen assembly enables fluid hold-up in the screensand initiation of the pulsing of liquid structures through the reactionchamber at operational conditions.

The preferred substantially rectangular-wave shaped screens in theremainder of the reaction chamber have 12×12 openings/square inch,0.060″ apertures, 0.023″ wire diameter, and 52% open area in order topropagate the pulses through the reaction chamber at lower pressure dropthan pulse-generation screens and allow for optimal contact time betweenthe gas and liquid phases.

Although screens with substantially square wave cross-sections areshown, screens with substantially rectangular cross-sections can also beused (See FIGS. 12-15).

How Pulsing and Regeneration are Achieved

Although overall liquid-gas molar flow rate ratios are comparable toconventional contactors, solvent volumetric flow rate in the absorber asdescribed herein is not constant. Rather, solvent volumetric flow rateinitially is low and a fraction of the solvent accumulates in thescreens as described above. Upon reaching a critical saturation, a largefraction of the accumulated solvent travels downstream at highvolumetric flow rate in a pulse. After the pulse, the solvent volumetricflow rate is low again until another pulse occurs. This repeats adinfinitum.

We have derived the following working parameters for achieving orinducing, and maintaining solvent pulsing:

Gas stream flow rates—>0.5 m/sMolar liquid/gas ratio—>2Screen opening size—0.040″ to 0.150″Wire diameter—0.020″ to 0.050″Spacing between screens—0.25″ to 1.50″Square wave height—0.25″ to 0.75″Screen specs for pulsing (FIG. 10A):

Openings/sq. in, wire diameter, opening size, open area ratio

-   -   12×12—0.028″—0.055″—44%        Pulse frequencies at 2.5 m/s Vgas:

Generation frequency—approximately 2/sec

Regeneration frequency—approximately 60/sec

This pulsing is beneficial because at flow rates and liquid-gas ratiossimilar to that of conventional columns the Reynolds number for theliquid places it squarely in the laminar regime. However, because theabsorber experiences the pulsing phenomenon, it greatly increases thevolumetric flow rate during a pulse bringing it more in line withturbulent flow. There exists numerous literature that show turbulentflow causes better mixing, which increases the rate of mass transfer.Furthermore, high speed photography shows pulsing enhancing theformation of micro-froth. Literature also exists that show froth andbubble structures enhance contact area. The use of co-current flow andthe geometry of the screens allow for these important solvent pulses tooccur.

Screen specs. For propagation (FIG. 10A):12×12 openings/square inch, 0.023″ wire diameter, 0.060″ opening size,52% open area ratioApproximately (4) ridges/inch across the diameter of the screens: ⅛″ridges and ⅛″ valleyse.g.—4″ diameter screen has 16 ridgesRidge height . . . 0.275″-0.375″Screens separated by 0.25″ spacers

FIGS. 12-15 illustrate various preferred cross-sectional screen designshaving a substantially rectangular cross-section which will cause“solvent pulsing” under proper conditions.

FIG. 12 is a square wave pattern, with the side walls 1661 of the samelength as the generally horizontal tops 1662 and bottoms 1663.

FIG. 13 shows screen 1760 with a rectangular pattern with side walls orvertical segments 1761 having a smaller length than the tops 1762 orbottoms 1763. Angle E in FIG. 13 (not to scale) illustrates that sidewalls 1761 may be inclined slightly, plus or minus 5°, relative to thedirection of flow of the gas stream, which in FIG. 13 is parallel tosidewall 1761. Similarly, angle F (not to scale) illustrates how tops1762 and bottoms 1763 may be inclined slightly, plus or minus 5°,relative to a plane perpendicular to the gas stream flow direction, suchplane shown by horizontal tops 1762 and horizontal bottoms 1763.

FIG. 14 shows screen 1860 with a rectangular pattern wherein side walls1861 are longer than horizontal tops 1862 and bottoms 1863.

FIG. 15 shows screen 1960 having rounded corners 1965 between side walls1961, horizontal tops 1962 and bottoms 1963.

It is to be understood that FIGS. 12-15 are by way of example, andnumerous other shaped screens may be utilized. We have found that themost preferred screen shape for inducing “solvent pulsing” is the“substantially rectangular or square wave cross section” shown in FIGS.10A, 10B, 12, 13 and 14. We believe the corners formed between the topsurface of each wave and the side walls extending downwardly there fromform a “first region” of the screen to which the froth adheresmomentarily (see FIG. 16C). Also, the bottoms of each square wave form a“second region” which allows the gas stream to increase in velocity, asthe first region limits flow (see FIG. 16C). If the flat tops andbottoms are within five degrees (5°) of being perpendicular to the flowdirection of the gas stream, and if the sidewalls are flat and withinfive degrees (5°) of the flow direction of the gas stream, we are ableto induce and maintain “solvent pulsing” reliably. Utilizing screenshaving “substantially rectangular or square wave cross section” withproper design and gas stream flow rates, “solvent pulsing” can beinduced and maintained in the embodiments shown in FIGS. 1, 5, 9, 10A,10B and 20.

If the side walls form an angle A between 5° and 20°, what we define asa “ridge shaped screen” is formed, and “solvent pulsing” is moredifficult to induce and maintain, but even without “solvent pulsing,”higher levels of efficiency can be attained than in prior art absorbers.

FIGS. 16A-16F illustrate how the pulsing occurs.

FIGS. 16A-16F illustrate the “solvent pulsing” phenomenon created inscreens 1360 illustrated in FIG. 10A. A single screen 1360 is shown inFIGS. 16A-16F as a solvent pulse is created in that single screen.

As shown in FIG. 16A, screen 1360 is referred to herein and in theclaims as a “shaped screen having a substantially rectangularcross-section.” As shown in FIG. 16A, screen 1360 includes flat tops1360 b, flat bottoms 1360 a, and flat side walls 1360 c, which may be ofequal length. As shown in FIG. 16A, screen 1360 has vertical regions1360A that extend in a vertical direction, parallel with (or within 5°of) the direction of gas stream 1330. In addition, regions 1360 b of thesurface of screen 1360 have a surface extending in a directiontransverse or perpendicular (or within 5° of transverse orperpendicular) to the direction in which gas stream 1330 flows.

FIG. 16A illustrates the first step in the “solvent pulsing” phenomenon.Aqueous froth comprising solvent bubbles and micro-droplets isaccumulating, or holding up, below the top surface 1360 b of each squarewave. Gas stream 1330 is flowing at a normal velocity through the tops1360 b and bottoms 360 a of each square wave. Gas flow 1330 a below ordownstream of screen 1360 is turbulent.

As shown in FIG. 16B, more solvent froth 1390 accumulates on firstregions of each screen, those regions being the outer edges of the top1360 b restricting the available opening at the center of each top 1360b through which the gas stream flows. This in turn causes the velocityof incoming gas stream 1330 to further increase, as shown by largerboldness of the arrows 1399 illustrating the flow of gas stream 1330.Turbulence of gas stream 1330 below screen 1360 increases.

FIG. 16C illustrates maximum hold-up or accumulation of solvent froth onscreen 1360. The solvent froth tends to accumulate beneath the top 1360b of each square wave, and along each side wall 1360 c connected to top1360 b; this area is the “first region” of each screen in which theaccumulation occurs. Gas velocity and turbulence below screen 1360 ismaximized as gas if forced to flow only through second regions definedas the bottoms 1360 a of each square wave.

FIG. 16D illustrates the initial phase of “solvent pulsing.” Clumps 1395of solvent froth are abruptly and violently torn from beneath the top1360 b of each square wave and flow downwardly into the violentturbulence 1399 below screen 1360. The “solvent pulsing” shown in FIG.16D maximizes 2 phase mixing between gas stream 1330 and solvent clumps1395 and between gas stream 1330 and solvent bubbles and micro-dropletsthat are not part of clumps 1395.

FIG. 16E illustrates the second phase of “solvent pulsing” whereinsolvent froth clumps have moved downwardly below screen 1360 asufficient distance that gas stream 1330 b begins flowing through openregions near the center of tops 1360 b. The clumps or pulses of solvent1395 cascade downstream and increase solvent turbulence and 2 phasemixing downstream.

FIG. 16F illustrates the status of gas stream flow and solvent frothaccumulation returning to the state shown in FIG. 16A after the solventpulses or clumps 1395 have moved downstream. The cycle shown in FIGS.16A through 16F repeats itself continually so long as the requisiteconditions of gas stream flow and solvent froth flow remain in effect.

As illustrated in FIG. 17, solvent pulse generation is controlled by aspecific set of screens. The key process responses are the minimum gasvelocity required to generate pulses (Vponset) and the pressure drop perunit packing depth (delP/m, measured in kPa/m). The critical screenparameters include screen opening size (in), the wire diameter (in) andthe wave height size (cm). By “wave height,” we mean the size of thesidewalls of each wave.

FIG. 18 below shows the relationship between the key process responsesand the critical screen parameters. As shown by FIG. 18, the absorberoperates in two major modes. Pulsing mode, described above andnon-pulsing or trickle flow mode. There is a region between these twomodes where the absorber operates in a transition mode with poorlydefined pulses. The impact on mass transfer can be observed by FIG. 18.This data was generated using a 35% Sodium Glycinate solution runningwith a molar liquid to gas ratio of 5 in an absorber with 1.6 m ofpacking. The data shows the % CO2 capture using an input CO2concentration of 9%. Normally it would be expected that higher % capturewould be observed at lower gas velocity because there is more contacttime between the target gas and the solvent but in this case, due to thepoor pulsing characteristics at lower gas velocity, lower % capture isobserved at lower gas velocity and the ideal best mass transfer occursat higher gas velocity.

FIG. 19 compares the present absorber operating in Co-current pulsingmode to a conventional countercurrent absorber using Monoethanolamine(MEA) solvent. Even though the two absorbers are of comparable packingdepth the present absorber demonstrates at least a 2× improvement in %capture.

FIG. 20 is a schematic showing solvent plug pulses 1451 and 1452 movingdownwardly through reaction vessel 1420. Since the plug pulses extendfrom sidewall 1421 to sidewall 1422, “channeling” of gas stream 1430through vessel 1420 is prevented, i.e. the gas stream components 1431,1432 and 1433 move downwardly at the same speed. The “plugs” 1451 and1452 prevent any of the gas stream components from flowing at a muchhigher speed than other components, which is “channeling” and whichsubstantially reduces efficiency.

FIG. 21 is a schematic illustrating the prior art problem of“channeling.” A counter-flow absorber 2120 is shown with gas stream 2130flowing upwardly. Solvent 2150 is sprayed into the top portion ofabsorber 2120. The gas stream tends to follow the path of leastresistance, resulting in a very high speed flow 2135 through the centerof absorber 2120. The extremely high flow rate reduces efficientlygreatly. The present invention eliminates this “channeling” problem.

FIGS. 22 and 23 are photographs taken of an absorber 2420 of the presentinvention. The bright area 2421 in FIG. 22 represents a screen 2460 onwhich little or no solvent froth has accumulated; light flows throughthis section and screen 2460 easily. That same screen 2460 becomes dark,and does not transmit light easily as shown in FIG. 23, as solvent frothplus pulse 2470 accumulates on screen 2460. Gas stream 2430 flowsdownwardly through absorber 2420.

FIG. 24 is a schematic representation showing how the photos in FIGS. 22and 23 were taken. Screens 2460 were placed in transparent vessel 2420.Gas stream 2430 and solvent 2450 were introduced and “solvent pulsing”was induced. If a screen in the transparent vessel was free of solvent,light from bulb 2499 passed through easily. The photo taken by camera2498 would show that segment as very bright.

Where a solvent pulse 2470 passes through the vessel, the pulse blocksthe light and that section of the transparent vessel appears dark.

Videos taken with this set-up verified the formation of “solvent pulses”and the formation of “plug pulses” described above.

Technical Description of Process

Gas/liquid absorption is a very common chemical process for using aliquid absorbent to remove a component from a gas stream or vice versa.Absorbers are used in natural gas processing, oil refining, chemical andpetrochemical industries, pharmaceuticals, fertilizers, etc.Applications include;

-   -   Removal of contaminants such as CO₂, H₂O, or H₂S from gas        streams    -   Removal of contaminants from a liquid stream using gas as the        absorbent

The absorbers shown and described herein can be used in all gas/liquidabsorption applications.

Conventional absorbers use an absorbent solvent and packing to createsurfaces through which mass transfer occurs. Liquid absorbent enters atthe top of the absorber vessel and is distributed evenly across the fullcross-sectional area of the packing using mechanical distributors. Thereare several types of packing, including random and structured. Randompacking is made up from individual pressed metal, ceramic, or plasticshapes that are randomly dumped onto a support tray in the absorbercreating a “packed bed”. Structured packing is corrugated segments ofmetal or plastic formed into a structure with intricate surface area,located inside the absorber.

Alternatively, absorbers may use trays or plates which force contactbetween the target gas and solvent. A trayed absorber uses perforatedplates, bubble caps or a valve tray to allow the gas to bubble upthrough the liquid absorbent to facilitate mass transfer. Mass transferoccurs as the absorbent liquid, draining downward from the top, contactsthe target gas, flowing upward from below, as the gas bubbles throughthe perforations. A third type of absorber is a “spray tower” where theliquid absorbent is sprayed downward to create small droplets, therebycreating surfaces for mass transfer. The solvent droplets fall downwardas the gas flows upward through the tower.

Large diameter absorbers (15 m) for gas/liquid absorption havedifficulty maintaining an even and consistent gas and liquid flows overthe cross-sectional area of the absorber. This results in channeling ofthe gas flowing upward through the liquid absorbent flowing downward,which in turn, leads to poor mass transfer.

In the present absorber, the gas passes down through the screens mixingwith the liquid and in doing so forms an aqueous froth consisting ofbubbles and droplets which create a very large surface area for masstransfer. But instead of leaving the bubbles and droplets intact in aconfined space which would produce a relatively static, fixed surfacearea similar to prior art devices, the present invention continuouslyand violently ruptures or fragments and reforms the bubbles and dropletsat a rapid rate. Some of the bubbles are caused to burst formingthousands of microscopic droplets from each bursting bubble whereby theactive surface area of the liquid solvent is further increased. Thishigh frequency and continuous regeneration of the surface of the liquidsolvent is a significant aspect of the invention. An enormous reactionsurface is created in a small volume. The reaction surface iscontinuously and violently ruptured and reformed to maximize theefficiency of the mass transfer.

The present absorber embodiment incorporates multiple gas absorber tubesin a modular design. The absorber tubes are optimized for consistent gasand liquid flow over the tube's cross-sectional area. Thecross-sectional area of the absorber tubes can be cylindrical, square,rectangular, triangular or polyhedral. The exact shape is optimized foreach application. The gas absorber tubes can be made out of metals,plastics, or ceramics to suit the process conditions. The individual gasabsorber tubes are densely mounted onto, or through, horizontal bulkheadplates that divide the reaction chamber into vertical stages. A portionof the flow passes through each of the absorber tubes, maintainingconsistent even flow over the cross-sectional area of the reactionchamber. This is just one feature of the design.

One application of the absorbers described herein is the removal of CO₂from a gas stream. In this application it is anticipated thatprecipitating solvents will be more economical than non-precipitatingsolvents for large scale. CO₂ capture, however in conventionalpacked-bed absorbers, the intricate structure and tortuous passagewaysthrough the random packing prevents the use of precipitating solvents.

In all embodiments, the liquid-to-gas contact surface area is increasedvia the creation of an aqueous froth which consists of droplets andbubbles instead of an intricate mechanical structure. The bubblesdroplets, bursting bubbles, and micro-droplets provide highliquid-to-gas surface area between the solvent and target gas. Vortextubes, detached eddies, and separated shear layers mix solvent with thetarget gas in the turbulent regime in-between the froth-generatorplates. Micro-mixing of the droplet and bubble structures facilitatesefficient absorption of the target gas.

When precipitating solvents are used, the absorbers of the inventionoperate without the precipitants blocking the absorber

The specifically designed mechanical substrate (or screen) generates anaqueous froth with a large and intricate gas/liquid interfacial area. Inconventional counter-current flow packed bed towers used for gasabsorption, solvent drains down in a trickle mode over random orstructured packing that forms the mechanical substrate while the gasflows upward from the bottom to the top of the tower. The limitedgas/liquid interfacial area consists of the wetted packing and liquidfilaments formed between individual elements or structure of the packingby the liquid solvent draining over the substrate.

The substrate of the present absorber consists of a plurality ofcorrugated screens that are separated by spacers. The screens arespecifically designed to create an aqueous froth and optimize solventpulsing. Bubbles are formed as the solvent and gas flow through thescreen openings. The bubbles combine to form aqueous froth. Theliquid/gas interfacial area formed by the wetted substrate or screen ofthe absorber is increased exponentially by the formation of the aqueousfroth and micro-droplets produced by bursting bubbles and the gas flowshearing solvent droplets from the wires of the screens.

The substrate or screen is optimized to form solvent plug pulses ofconsolidated froth matrices over the cross-sectional area of theabsorber chamber to prevent the gas flow from bypassing around thepulses. The corrugated screens form parallel ridges and valleys acrossthe area of the screens. The volume of space inside the valleys is onthe upstream side of the screens and the volume of space inside theridges is on the downstream side of the screens. As gas pressure dropsacross the screen, the valleys on the upstream side of the screens havehigher pressure than the ridges on the downstream side of the screens.The flow of gas and liquid is through the top of the ridges into theridges and through the bottom of the valleys into the space in-betweenthe screens, and through the walls of the ridges and valleys from thevalleys into the ridges.

The substrate consists of an initial set of pulse generator screensfollowed by a set of pulse propagation screens. The pulse generationscreens are generally closer together and have smaller screen openingsizes than pulse propagation screens, but also have higher pressure dropacross the screen. Pulse propagation screens have larger screen openingsand may be spaced further apart than the pulse generator screens,depending on the reaction kinetics of the solvent. Pulse propagationscreens are used to regenerate the reactant surfaces of the pulses andto reduce overall pressure drop across the column of screens in thereaction chamber. Once a plug pulse is formed in the pulse generatorscreens, momentum, energy from the gas flow, and the acceleration ofgravity (in vertical columns) advance the pulse through the pulsepropagation screens.

In the initial pulse generator screen, continuous streams of bubbles aregenerated as the gas and liquid flow through the screen openings in thetop and side walls of the square wave tops and through the screenopenings in the bottom of the square waves. The bubbles combine in theridges and in-between the screens to form a continuous flow of aqueousfroth to the second pulse generator screen. In the second pulsegenerator screen, a portion of the froth generated as the gas and liquidflow through the screen openings in the ridges are held up inside theridges. As more froth is held up in the ridges across the area of thescreen, the flow resistance through the screen increases until a portionof the froth being held up in the ridges is released or projected out ofthe ridges as a pulse of aqueous froth that is a portion of the area ofthe screen. As the hold-up and pulsing phenomena occurs in the next fewdownstream screens, the aqueous froth pulses consolidate to cover theentire cross-sectional area of the screens, forming a plug pulse asshown in FIG. 11D. The plug pulses advance through the downstream pulsepropagation screens and prevent the gas flow from bypassing around thesolvent pulses.

The liquid/gas interfacial area of the aqueous froth is regenerated athigh frequency. Depending on the pulse velocity and the spacing betweenthe screens, the interfacial area can be regenerated up to 100 times persecond.

As the target gas is absorbed into the solvent, the concentration of thereactant species in the solvent is depleted at the interface therebyreducing the driving force of the reaction. The liquid phase resistanceto mass transfer increases, reducing the driving force between the twophases, and decreases the reaction kinetics between the gas and liquidphases. As the pulses of solvent advance through the reaction chamber,the liquid/gas interfacial area of the pulses is regenerated each timethe solvent pulse passes through a screen. Each time the liquid/gasinterfacial area is regenerated the local reactant surfaces arereplenished with the leanest solvent available at that stage of theabsorber. Replenishing the local reactant surfaces with lean solventincreases the differential concentration between the gas phase andliquid phase, decreases the liquid phase mass transfer resistance, andmaintains high reaction kinetics throughout the reaction chamber.

When lean solvent loads up with target gas molecules captured from themixed gas flow, the reactant species is depleted forming rich solvent.Rich solvent is regenerated by boiling off the target gas molecules, andthe lean solvent is recycled back into the absorber to capture more ofthe target gas. In some situations the reactant product formed by thechemical reaction can exceed the solubility limit and form aprecipitant. A precipitating solvent can be used in some applications tosignificantly reduce the cost of solvent regeneration by reducing theamount of liquid that has to be boiled to release the captured targetgas molecules from the rich solution.

Conventional counter-current flow packed bed towers clog up whenoperated with precipitating solvents. The present absorber can operatewith precipitating solvents that would clog a conventionalcounter-current flow packed bed tower. In the present absorber, thesolvent pulses that advance through the column of screens and arereformed at high frequency create a dynamic environment inside thereaction chamber that prevents precipitants from growing to a size largeenough to clog the mechanical substrate, and the momentum of the pulsesshear the precipitants off of the substrate.

In the present absorber the mechanical substrate or screens wetted bythe solvent forms a small portion of the total liquid/gas interfacialarea. The dynamic environment prevents precipitants from growing largeenough to clog the screen openings. The momentum of the pulsestransports the precipitants out of the reaction chamber. The leastdynamic zones in the absorber are the spaces between the spacers alongthe wall of the reaction chamber. But even these spaces are filled andemptied at high frequency as the pulses advance through the absorbercolumn, thereby preventing the buildup of precipitants in the spacesbetween the spacers along the walls of the reaction chamber. Themomentum of the pulses shear the precipitants off of the substrate,flush the spaces between the spacers along the walls of the reactionchamber, and transport the precipitants out of the reaction chamber.

Objects and Advantages

The liquid-to-gas surface area is increased using specifically shapedscreens to shatter or rupture the solvent into a myriad of dropletswhich create a very large surface area for mass transfer which is madeup of the solvent itself. But instead of leaving the small dropletsintact in a confined space which would produce a relatively static,fixed surface area similar to prior art devices, the present inventioncontinuously and violently ruptures and reforms the droplets at a rapidrate. Bubbles also form which in turn are caused to burst formingthousands of microscopic droplets from each bursting bubble, whereby theactive surface area of the liquid solvent is further increased. Thishigh frequency and continuous regeneration of the surface of the liquidsolvent is a significant aspect of the invention. An enormous reactionsurface is created in a small volume. The reaction surface iscontinuously and violently ruptured and reformed to maximize theefficiency of the mass transfer. The huge surface area provided by thesedroplets and bubbles for mass transfer, combined with its unstablenature means that droplets and bubbles are reformed before mass transferequilibrium is reached.

In other words, concentration of the component absorbed into solvent isstill low when the droplets are reformed. Thus the concentrationgradient, i.e. the difference between the concentrations of the targetcomponent in the gas, compared to the solvent, is still high. Thedynamic reaction surface area is then reformed with lean solvent (i.e.solvent with a lower concentration of the absorbed component), therebycreating a high concentration gradient between the target gas and thesolvent. The high concentration gradient maximizes the driving force formass transfer.

The reactant surfaces are reformed at frequent intervals. Rich solventis replaced with leaner solvent flowing down the tube. The reactantsurfaces are reformed and replaced each time a pulse passes through oneof the screens.

The absorbers can be designed to operate within the parameters requiredfor optimal gas absorption of a variety of commercial and generic,precipitating and non-precipitating absorbent solvents which have arange of viscosities, surface tensions, and specific gravities.

Individual gas absorber tubes are densely packed into each stage of theFTGA embodiment. The stages are flooded with solvent to a predeterminedlevel above the multiple solvent injection ports in the gas absorbertubes or to the top of the tubes themselves such that solvent isintroduced at a predetermined rate into the gas absorber tubes in eachabsorber stage.

Screens may be used in combination with solvent distribution plates.These plates serve to assist in redistributing the solvent and gas asthey pass down the tubes.

The flow of mixed gases and solvent passes through screens, located atfrequent intervals in each froth generator assembly, in order to reformthe reactant surfaces of the droplets, bubbles, and micro-droplets. Richsolvent from the reactant surfaces is replaced with leaner solvent fromfluid structures in the flow field. These droplets, bubbles andmicro-droplets provide a high liquid-to-gas contact-area between thesolvents and the target gas.

The liquid/gas separators remove a portion of the rich solvent from theflow. Lean solvent introduced in the next absorber stage replaces theportion of rich solvent removed by the liquid/gas separators.

In order to be able use a variety of commercial and generic solventswhich all have a range of viscosities, surface tensions, and specificgravities, the absorber can be designed to operate within the parametersrequired for optimal gas absorption of specific solvents.

The size and number of the FTGA tubes, the mesh size of the screens andopen-area ratio of the screens are selected in order to balance pressuredrop with efficiency.

The distance between a screens and distributor plates is balanced withgas velocity and pressure drop to optimize system performance andremoval of the target impurity from the gas stream.

Similarly distance between screens is also balanced with therate-of-reaction to provide more or less time and distance for turbulentstructures to form and reactant surfaces to absorb the target gas athigh reaction rates.

It is believed that the following happens in the absorbers describedabove: In a packed bed, diffusive flow over random or structured packingconsists of a boundary layer wetting surface of packing, an intermediateflow regime, and a free surface flow exposed to gas. As layers of fluidmolecules flow over other layers of fluid molecules and turbulenceoccurs in flow between solid surfaces moderate mixing occurs between thesurface layer and the intermediate layer, but little mixing occursbetween the intermediate layer and the boundary layer. Molecularattraction of solid molecules is stronger than attraction of fluidmolecules so boundary layer remains relatively static. As reactant infree surface layer is exposed to target gas, reaction rate is limited toregeneration of fresh reactant surfaces exposed by moderate mixingbetween intermediate layer and free surface layer that is driven byturbulence and diffusive flow dynamics.

In a spray tower, currents in the free surface of falling dropletscaused by friction between the gas molecules and fluid molecules and, toa lesser extent, the Marangoni effect drive mixing between the freesurface layer molecules that have reacted with the target gas and freshreactant from inside the droplet.

The foregoing description of the invention has been presented forpurposes of illustration and description and is not intended to beexhaustive or to limit the invention to the precise form disclosed.Modifications and variations are possible in light of the aboveteaching. The embodiments were chosen and described to best explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best use the invention in variousembodiments suited to the particular use contemplated.

We claim:
 1. A method of absorbing a selected component from an incomingflowing gas stream, wherein said absorption occurs across the surface ofan aqueous froth comprising a liquid solvent for said selectedcomponent, said froth being intermixed with numerous bubbles andmicro-droplets formed from causing bubbles in said froth to burst, themethod comprising the steps of: flowing said gas stream downwardly intoa reaction vessel; providing a plurality of mesh assemblies in andacross said reaction vessel, said mesh assemblies comprising shapedscreens having substantially rectangular wave cross-sections whereinsaid mesh assemblies are spaced apart vertically from one another intiers along the height of said reaction vessel, causing said solventfroth and micro-droplets to flow co-currently with said incoming gasstream and to accumulate rapidly and periodically on first regions ofsaid shaped screens, thereby limiting the flow of said gas streamthrough said first regions, and causing increased velocity of said gasstream through second regions of said shaped screens; causing said rapidperiodic accumulations of solvent froth and micro-droplets toperiodically and abruptly separate in clumps from said first regions ofsaid shaped screens to achieve solvent pulsing, and to cause said clumpsto flow downstream from each tier of said plurality of shaped screenstoward another tier of shaped screens maximizing the turbulence in thegas stream downstream of each tier of shaped screens by the suddenperiodic and abrupt separation of the accumulated clump of solvent frothand micro-droplets from said tier of shaped screens; minimizing the sizeof said solvent bubbles and the size of micro-droplets as said gasstream moves through each of said plurality of spaced apart tiers ofscreens by causing each tier of screens to burst any of said solventbubbles of a given size in order to reform said solvent froth at eachtier of screens to maximize the total surface area of said solventfroth, thereby maximizing the mass transfer between the incoming gasstream and said solvent froth and micro-droplets by the use of solventpulsing.
 2. The method of claim 1 wherein the preferred range of solventpulsing frequency is between 1 and 20 pulses per second.
 3. The methodof claim 1 wherein the most preferred range of solvent pulsing frequencyis between 2 and 10 pulses per second.
 4. The method of claim 1 whereinsaid tiers of screens are preferably sized and spaced to causereformation of said solvent froth between 30 and 100 times per second.5. the method of claim 1 wherein said tiers of screens are mostpreferably sized and spaced to cause reformation of said solvent frothbetween 50 and 80 times per second.
 6. The method of claim 1 whereinsaid shaped screens have substantially square-wave or rectangular-wavecross sections.
 7. The method of claim 1 wherein said solvent froth andmicro-droplets accumulate simultaneously across the width of said shapedscreens and abruptly separate across the width of said shaped screens toform solvent plugs extending across the width of said reaction vessel.8. The method of claim 1 wherein a precipitating solvent is utilized andcomprising the further step: preventing the clogging of said reactionvessel by solvent precipitants by minimizing the size of said solventbubbles and micro-droplets, droplets and by creating a dynamicenvironment in which the bubbles and droplets are continuously andviolently fragmented and reformed at a rapid rate, thereby limiting thesize that the precipitants can grow.
 9. The method of claim 1 wherein aprecipitating solvent is utilized and comprising the further step:transporting the precipitants out of the reaction chamber with themomentum of the solvent pulses and the co-current flow of the gas andliquid phases, thereby preventing the clogging of said reaction vesselby solvent precipitants.
 10. The method of claim 1 wherein said gasstream flow rate is greater than 0.5 meters/second, the screen openingsize is between 0.040 inch and 0.150 inch, the screen wire diameter isbetween 0.020 inch and 0.050 inch, the spacing between screens is 0.25inch to 0.75 inch and the height of each of said substantially squarewaves of said screens is between 0.25 inch and 0.75 inch.
 11. The methodof claim 1 wherein said reaction vessel has first and second chamberswherein said first chamber has an inlet end for said flowing gas streamand an outlet end for said flowing gas stream, said outlet end having abulkhead plate extending across the reaction vessel to separate saidfirst chamber from said second chamber of the reaction vessel, andwherein a plurality of absorption tubes extends through said bulkheadplate and provides fluid communication between said first chamber andsaid second chamber.
 12. The method of claim 11 wherein each of saidabsorption tubes extends vertically and carries a plurality of spacedapart, shaped screens.
 13. Apparatus for absorbing a selected componentfrom a gas stream via a method in which absorption occurs across thesurface of a froth comprising, a liquid solvent for said selectedcomponent, said froth being intermixed with numerous micro-dropletsformed by causing bubbles in said froth to burst, the apparatuscomprising a vertically oriented reaction vessel having a top, a bottom,and side walls forming a reaction chamber, said chamber being fluidlyconnected to a gas inlet for the flow of said gas stream downwardly intosaid reaction chamber, the apparatus being characterized by: means fordistributing liquid solvent downwardly into said reaction chamber, aplurality of vertically spaced apart screens in said reaction chamber,wherein each of said screens extends horizontally from side wall to sidewall, across the vertical cross-section of said reaction chamber. 14.The apparatus of claim 13 wherein said reaction vessel is cylindricaland wherein said screens each extend the full diameter of said vessel.15. The apparatus of claim 14 wherein each of said screens is a shapedscreen having a substantially rectangular wave cross section.
 16. Theapparatus of claim 15 wherein each of said screens has a substantiallysquare cross section.
 17. The apparatus of claim 13 further comprisingmeans for creating periodic solvent pulsing in said reaction chamber.18. Apparatus for absorbing a selected component from a gas stream via amethod in which said absorption occurs across the surface of a frothcomprising, a liquid solvent for said selected component, said frothbeing intermixed with numerous micro-droplets formed by causing bubblesin said froth to burst, the apparatus comprising a reaction vesselhaving a first chamber and a second chamber separated by a bulkheadplate extending across the reaction vessel, said chamber being fluidlyconnected to a gas inlet for the flow of said gas stream into the firstchamber, the apparatus being characterized by: an array of discrete,vertically oriented absorption tubes carried in respective flow portsformed through said bulkhead plate, each said absorption tube extendingthrough said bulkhead plate into said first chamber to define arespective conduit for the flow of said gas stream from said firstchamber into said second chamber, said flow ports and absorption tubesbeing sized and positioned to equalize the flow speed of said gas streamdownwardly through each said absorption tube from said first chamberinto said second chamber, a plurality of vertically spaced apart meshscreens provided in each of said absorption tubes, the mesh screens ineach absorption tube extending transversely between sidewalls of eachsaid tube, means for injecting said liquid solvent into each saidabsorption tube; and means for pressurizing said gas stream in saidfirst chamber to thereby cause a back pressure in said first chamber,which in turn causes said gas stream to flow at substantially equal flowrates through each of said absorption tubes into said second chamber.19. The apparatus of claim 18 wherein said reaction vessel is a verticalvessel and wherein said gas stream flows downwardly through said vessel.20. The apparatus of claim 18 wherein said means for injecting liquidsolvent into each absorption tube injects solvent downwardly into eachtube.
 21. The apparatus of claim 18 wherein said means for injectingliquid solvent includes a reservoir of solvent above said bulkhead plateand between said absorption tubes.
 22. The apparatus of claim 18 whereinsaid reaction vessel is a horizontal vessel.
 23. The apparatus of claim18 wherein each of said plurality of mesh screens is a corrugatedscreen.
 24. The apparatus of claim 18 wherein each of said plurality ofmesh screens has a substantially rectangular wave cross-section.
 25. Amethod of absorbing a selected component from an incoming flowing gasstream, wherein said absorption occurs across the surface of an aqueousfroth comprising a liquid solvent for said selected component, saidfroth being intermixed with numerous bubbles and micro-droplets formedfrom causing bubbles in said froth to burst, the method comprising thesteps of: flowing said gas stream downwardly into a reaction vessel;providing a plurality of mesh assemblies in and across said reactionvessel, said mesh assemblies comprising shaped screens havingsubstantially rectangular wave cross-sections wherein said meshassemblies are spaced apart vertically from one another in tiers alongthe height of said reaction vessel, causing said solvent froth andmicro-droplets to flow co-currently with said incoming gas stream,minimizing the size of said solvent bubbles and the size ofmicro-droplets as said gas stream moves through each of said pluralityof spaced apart tiers of screens by causing each tier of screens toburst any of said solvent bubbles of a given size in order to reformsaid solvent froth at each tier of screens to maximize the total surfacearea of said solvent froth, thereby maximizing the mass transfer betweenthe incoming gas stream and said solvent froth and micro-droplets. 26.The method of claim 25 wherein said tiers of screens are preferablysized and spaced to cause reformation of said solvent froth between 30and 100 times per second.
 27. the method of claim 25 wherein said tiersof screens are most preferably sized and spaced to cause reformation ofsaid solvent froth between 50 and 80 times per second.
 28. The method ofclaim 25 wherein a precipitating solvent is utilized and comprising thefurther step: preventing the clogging of said reaction vessel by solventprecipitants by minimizing the size of said solvent bubbles andmicro-droplets, droplets and by creating a dynamic environment in whichthe bubbles and droplets are continuously and violently fragmented andreformed at a rapid rate, thereby limiting the size that theprecipitants can grow.
 29. The method of claim 25 wherein aprecipitating solvent is utilized and comprising the further step:transporting the precipitants out of the reaction chamber with themomentum of the solvent pulses and the co-current flow of the gas andliquid phases, thereby preventing the clogging of said reaction vesselby solvent precipitants.
 30. The method of claim 25 wherein said gasstream flow rate is greater than 0.5 meters/second, the screen openingsize is between 0.040 inch and 0.150 inch, the screen wire diameter isbetween 0.020 inch and 0.050 inch, the spacing between screens is 0.25inch to 1.50 inch and the height of each of said substantially squarewaves of said screens is between 0.25 inch and 0.750 inch.
 31. Themethod of claim 25 wherein said reaction vessel has first and secondchambers wherein said first chamber has an inlet end for said flowinggas stream and an outlet end for said flowing gas stream, said outletend having a bulkhead plate extending across the reaction vessel toseparate said first chamber from said second chamber of the reactionvessel, and wherein a plurality of absorption tubes extends through saidbulkhead plate and provides fluid communication between said firstchamber and said second chamber.